Automation systems may be used to automatically control a variety of activities, such as turning lights and appliances on and off. Typically, the electrical devices controlled by the system are driven by standard alternating current power lines. Individual relays are coupled in series with each of the devices in order to control the power supplied to several different loads. Each of the relays may be operated under control of a device, such as a host computer which controls each channel of the system. These signals are used to control the relay in order to set the level of power supplied to each load.
Several difficulties are encountered in constructing such a system. For example, typically three wires are required to transmit the necessary control signals for each channel, i.e. for each device to be controlled. The large number of control lines resulting from use of many different channels increases the complexity in installation and the risk that one of the control lines may be interrupted, thereby preventing automated operation of a load. Furthermore, the control signals must be carefully generated in order to operate properly. For example, lights may flicker if the control voltage is not synchronous with the power supply.
Another difficulty is maintaining flexibility in the system. While a system may be designed which is well suited to a particular environment, it may be troublesome to adapt the system to another environment. For example, one environment may require control of only lights, radios or other light loads, while another may require control of light and heavy loads, such as water heaters or the like.
Convenience in servicing the system is still another practical consideration. Even the best-designed systems may occasionally fail. Thus, there is a need to ensure that the elements which have failed may be quickly located and easily replaced. Further, it is desirable to provide a means for operating the devices normally controlled by the system at times when the system is down.
Therefore, there is a need to provide a means which reliably controls the power supplied to a wide variety of devices according to signals supplied from a processor device. There is a further need to furnish a power control system which is convenient to use and adaptable to different environments. Finally, there is a need for a power control system which is easily installed and serviced, and which permits back-up control if the system fails.